Platinum-impregnated catalysts

Dorado E, de Lucas-Consuegra A, Vemoux P, Valverde JL (2007) Electrochemical promotion of platinum impregnated catalyst for the selective catalytic reduction of NO by propene in presence of oxygen. Appl Catal B Environ 73 42-50... 

Fig. 3. Electron micrograph of 2.5% (w/w) platinum/silica catalyst. Prepared by impregnation with chloroplatinic acid, reduced in hydrogen at 210°C. Micrograph obtained by thin sectioning. The black dots are platinum particles. (X 100,000). Reproduced with permission from T. A. Dorling and R. L. Moss, J. Calal. 7, 378 (1967) R. L. Moss, Platinum Metals Rev. 11 (4), 1 (1967), and British Crown Copyright.

To date, the only shock tube apparatus equipped to study surface reactions is the KIST facility at ATK GASL in New York. The tests done so far have studied methane oxidation, CFI4 + 2O2 CO2 + 2H2O on the surface of an SCT ferrous-based reactor impregnated with platinum based catalyst. To isolate the effects of the screen and the catalyst on the reaction, three types of tests were run catalyzed screen with combustible gases,... 

Fig. 2. Isomerization of n-heptane over mixtures of particles of silica-alumina and particles of inert-supported platinum (W5). The dashed lines represent conversions over platinum-impregnated silica-alumina. Conditions of runs 25 atm., Hj/nC = 4/1, space velocity = 0.7 g. nC7 per hour per gram of catalyst.

Commercial zeolite based hydroisomerization catalysts comprise alumina bound and platinum impregnated dealuminated mordenite. The activity and selectivity of the hydroisomerization of n-paraffins is strongly influenced by acid leaching. The influence of silica to alumina ratio has been studied for pentane isomerization over platinum mordenite many times since one of the first papers published (6). 

Platinum catalysts were prepared by impregnation of formed supports with reverse microemulsions (water-in-oil) or water containing chloroplatinic acid. Microemulsion catalysts were more active in combustion of toluene in toluene-air mixtures than those prepared classically from water solutions. The size of platinum in classically impregnated catalysts was three times higher than that of the catalysts prepared from microemulsions. In the case of microemulsion preparation method, platinum is located near the pellet surface or its position in the pellet can be optimised. The viscosity of the microemulsion affects the concentration profile of platinum in the catalysts. 

For catalysts that were simply dried in air at 110°C after impregnation of the alumina with H2PtClfe and Re207, it was concluded that a platinum-rhenium alloy formed on reduction. This conclusion was based on the observation that the presence of platinum accelerated the reduction of oxygen chemisorbed on the rhenium and on results showing that the frequencies of the infrared absorption bands of carbon monoxide adsorbed on platinum and rhenium sites in platinum-rhenium catalysts were different from those found with catalysts containing only platinum or rhenium. However, for catalysts calcined in air at 500°C prior to reduction in hydrogen, it was concluded that the platinum exhibited much less interaction with the rhenium (66,71). 

The T50 activity of impregnated y-alumina spheres is plotted vs. palladium content in Figure 4. Pure palladium catalysts as well as platinum and palladium co-impregnated catalysts were tested. When palladium concentration was increased above 0.03 wt %, there was no further increase in CO oxidation activity. Furthermore, the activity of catalysts containing both platinum and palladium, with the platinum palladium weight ratio varying tenfold, was virtually unaffected by the presence of platinum. 

In this paper we investigated the properties of three-way automotive Pt-Rh / Al203-Ce02 catalysts prepared either by simultaneous impregnation of the two noble metals (coimpregnation = Cl) or by the technique of successive impregnations (S.I.). Their catalytic performances were measured after reduction or calcination at 500°C, for the oxidation of a propane-propene mixture under lean conditions and for the reduction of NO by CO under stoichiometric mixtine. Monometallic platinum catalysts and an alumina supported bimetallic platinum-rhodium catalyst were also prepared for a comparative study. ... 

---